This invention relates generally to calculators and more particularly to programmable electronic calculators in which keyboard operations become program instructions. In this particular type of calculator no special language is required. When a key is pressed one program step is completed. Programmable electronic calculators generally utilize memories which enable them to store instructions and data for repetitive and iterative solution. In order to enter the program into memory the user depresses the calculator keys in a given sequence. The result of each sequence step may be displayed for the convenience of the user as he progresses through his calculation. The key code for each program step may also be displayed. Key codes generally are alphanumeric representations of the keys on the keyboard. If the user wishes to modify or edit his program after initial entry into memory he must precisely determine to which key he should return in order to implement the change. To make that determination for calculators constructed according to the prior art, the user had to refer to a separate machine unique association table and a program to determine the specific key to depress relative to a particular program step.
For programming convenience key codes and program line numbers should be easily interpreted by a user. An object of this invention is to improve the ease of program debugging and editing by introducing a programmable calculator which displays a key position on the keyboard and absolute program line numbers. A further object of this invention is to provide a calculator having a convenient way for a user to get to the top of memory and eliminate the need for an AND key or a RETURN key. The invention provides a programmable calculator having preprogrammed branch instructions to the top of memory.
A further object of this invention is to provide a calculator wherein a user can program a branch instruction to another place in the program by merely actuating a single key and entering a line number address of the branch destination. Another object is to increase the utilization of available program memory by merging key codes representing a plurality of actuated keys corresponding to a branch instruction.
A further object is to provide an improved error display wherein the invention displays and flashes the contents of a register within an operational stack.
Another object is to provide an improved display wherein the invention automatically changes its format when in underflow or overflow.